Many processes involve the transport of quantities of items in a conveying system. In some of these processes, it is useful to locate and measure physical edges on items. Once an edge has been detected and its sense (rising or falling) and height are determined, this detailed information can be interpreted to determine item or feature presence and position, the existence of overlayed or overlapped objects (such as labels or multiple items) and other feature information relevant to any particular application.
In applications involving the transport of quantities of items, there are advantages in having a low-cost detector capable of resolving edges down to or less than the thickness of a label or a piece of paper, determining the sense of the edge, and determining the height of that edge. Furthermore, there is a need for such capabilities in systems that handle tens of thousands of items per hour in a single stream.
Currently, simple detection systems for the detection of objects moving along a defined path are generally employed for counting the number of objects moving past a point on the path. This technology is suitable for counting "shingled" items (such as newspapers) on a conveyor. The detection method or apparatus typically provides for the illumination of the surfaces of the objects by one or more radiation sources. One or more light detection sensors are utilized for receiving the radiation reflected from these surfaces. A counting condition (for counting the number of objects) is detected when there is a decrease in the amount of light received by the light detection sensor or sensors.
The problem with the present object detection systems, however, is the failure to identify and distinguish between leading and trailing (or rising or falling) edges of an object as it passes the detection station. Current systems only provide a detection signal when the amount of reflected light detected at one sensor is different from the amount of reflected light detected at another sensor. Such systems do not provide a means for determining whether the edge of the object detected was either the leading edge or the trailing edge. Further, these systems do not provide a means for determining the height (thickness) of an edge. Accordingly, there is a need for an object edge detector capable of providing limited three-dimensional geometrical information of the detected object for distinguishing between leading and trailing edges of the object and for providing information about the geometry of the detected object.
At present, detectors capable of identifying, locating and measuring features such as edges either lack the ability to resolve very small features (e.g. acoustic or laser ranging); require elaborate lighting, large computational resources, or substantial time to develop a result (e.g. high-resolution imaging systems); or provide limited information (e.g. devices which measure thickness using light curtains and mechanical or opto-electronic item counters). No existing system capable of detecting edge presence, sense, and height combines the characteristics of low cost, high resolution, modest computational resources, and high speed.
In particular, there exists a need in the processing of mail and other documents to identify overlapped items, address windows and labels, and stamps. Further, there exists a need to employ a plurality of detectors to provide additional feature information on one or both sides of items transported in mail handling and other systems that transport quantities of materials. Such applications include the detection of multiples, improved optical character recognition (OCR) read rates (which depend on address block location--often associated with a window or label), and locating and/or verifying the presence of stamps or other features. Additionally, there is a need for an object detector capable of identifying overlapping objects having relatively uniform, flat surfaces.
Typical mail processing systems handle ten or more pieces of mail per second in a single stream. However, given presently available technology, their cost would be increased greatly by the addition of vision systems capable of the required resolution and throughput. Nor would the information provided by a simple edge detector (with no sense or thickness information) suffice to accurately distinguish features such as labels, windows, stamps, and envelope folds. Accordingly a novel approach to edge and feature detection is required to solve problems which currently exist in the handling of mail, other documents, and other materials with three dimensional surface features.